US3818273A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Barrier isolator device employing an overload protection circuit
Assignee: Yokogawa Electric Corp
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Filing: 1973-01-22
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Granted: 1974-06-18
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Expires: 1993-01-22
Abstract
Abstract A barrier isolator device is disclosed for interconnecting a voltage source in a safe area, a load (such as a sensing element) in a hazardous area, and a load-associated device (such as a recorder) in a safe area. The barrier isolator device includes an overload protection circuit arranged to transmit signals between the load and the load-associated device, a first isolating circuit connecting the voltage source with the overload protection circuit, and a second isolating circuit connecting the load-associated device with the overload protection circuit. The protective circuit is characterized by low voltage losses in normal operation, low power consumption in a fault condition, and automatic resetting. The protective circuit comprises a current control means, such as a transistor, in series with the load and controlling the current flowing through the load by varying its conductivity. A current detection means, such as a low valued resistor, is connected in series with the load to detect the predetermined limiting value of current, and a voltage detection means, such as a resistive voltage divider, is connected parallel to the voltage source for detecting the predetermined limiting value of voltage. The current control means is arranged to be responsive to the current and voltage detection means to react to either a current or voltage overload condition by reducing its conductivity to limit current flow through, and voltage across, the load. Under normal conditions the current control means inserts a conducting transistor''s collector-emitter circuit in series with the load, and the current detecting means inserts a low valued resistor in series with the load, and hence the overload protection circuit introduces only a small series voltage loss. The voltage detecting means places large valued resistors in parallel with the voltage source, and any bias voltages provided to the current control means by the voltage source can be supplied through similar large valued resistors, and hence there is little power consumption during a voltage overload condition. The current control means and the voltage and current detection means are arranged to automatically restore themselves when overload conditions vanish. Accordingly, the overload protection circuit is highly suitable for use in intrinsically safe circuitry arranged to prevent excess energy from entering a hazardous environment, such as an explosive environment.
Inventors
- 👤 T Nakashima
- 👤 S Ohta
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 13:47
CPC Classifications
H; H02; H02H; H02H9/00; H02H9/008
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
151 words
A barrier isolator device for interconnecting a voltage source in a safe area, a load in a hazardous area, and a loadassociated device in a safe area and arranged to prevent excess electrical energy from being applied to the load, comprising an overload protection circuit connected to the load and arranged to transmit signals between the load and the loadassociated device, and to prevent current and voltage in excess of independent predetermined values from being applied to the load; first current isolating means connecting the voltage source with the overload protection circuit for transmitting electrical power to the overload protection circuit; and second current isolating means connecting the load-associated device with the overload protection circuit and including a current transformer for transmitting signal changes between the load and the load-associated device, whereby transfer of excess electrical energy from the voltage source or from the load-associated device to the load is prevented.
Claim 2
Dependent Claim
151 words
A barrier isolator device for interconnecting a voltage source in a safe area, a load in a hazardous area, and a loadassociated device in a safe area and arranged to prevent excess electrical energy from being applied to the load, comprising an overload protection circuit connected to the load and arranged to transmit signals between the load and the loadassociated device, and to prevent current and voltage in excess of independent predetermined values from being applied to the load; first current isolating means connecting the voltage source with the overload protection circuit for transmitting electrical power to the overload protection circuit; and second current isolating means connecting the load-associated device with the overload protection circuit and including a current transformer for transmitting signal changes between the load and the load-associated device, whereby transfer of excess electrical energy from the voltage source or from the load-associated device to the load is prevented.
Claim 3
Dependent Claim
119 words
A barrier isolating device as claimed in claim 1 wherein said overload protection circuit comprises: voltage detection means connected in parallel with the voltage source for detecting said predetermined value of voltage, current detection means connected in series with the load for detecting said predetermined value of current, and current control means connected in series with the load for controlling the current flowing through the load, said current control means responding to the voltage detecting means and to the current detecting means by reducing its conductivity and therefore, the current flowing through the load, whenever either current or voltage is detected to be in excess of said predetermined values, thereby limiting the current and voltage applied to the load.
Claim 4
Dependent Claim
94 words
A barrier isolating device as claimed in claim 2 wherein said current control means comprises a controllable device presenting a variable conductivity in series with the load and having an input circuit arranged to receive bias signal causing the device to be conductive, and a control circuit connected to both the voltage detecting means and the current detecting means and having an output circuit connected to the input circuit of the controllable device and diverting the bias signal therefrom whenever either current or voltage is detected to be in excess of said predetermined values.
Claim 5
Dependent Claim
98 words
A barrier isolating device as claimed in claim 3 wherein said controllable device comprises a transistor with its collector-emitter circuit in series with the load, and means for supplying a source of bias current to its base to cause the transistor to conduct and wherein the output circuit of the control circuit is connected so as to shunt the base-emitter circuit of the transistor to divert the bias current from the base to cause the transistor to become non-conductive whenever the control circuit output circuit responds to detection of current or voltage in excess of said predetermined values.
Claim 6
Dependent Claim
37 words
A barrier isolating device as claimed in claim 4, wherein said control circuit comprises transistor means connected to said voltage and current detecting means and having its output circuit through the collector-emitter circuit of said transistor means.
Claim 7
Dependent Claim
109 words
A barrier isolating device as claimed in claim 3, wherein said controllable device comprises transistor means with its collector-emitter circuit connected in series with the load and means for supplying a bias current to its base to cause it to conduct, and a silicon controlled element in series with the load and having a gate terminal and means including said transistor means for applying a gating signal to said gate terminal, said control circuit being arranged to turn off said transistor means whenever either of current or voltage is determined to be in excess of said predetermined values, whereby said gating signal is removed from said silicon controlled element.
Claim 8
Dependent Claim
70 words
A barrier isolating device as claimed in claim 6 further comprising a resistor shunting the collector-emitter circuit of said transistor means, said shunting resistor being arranged to conduct a current below the holding current of said silicon controlled element, whereby said silicon controlled element turns off when said transistor means turns off, and whereby said silicon controlled element carries a greater portion of the overload voltage than said transistor means.
Claim 9
Dependent Claim
42 words
A barrier isolating device as claimed in claim 1 wherein said current control means comprises a control circuit with input transistor means, said voltage detecting means and current detecting means being applied to said current control means through said input transistor means.
Claim 10
Dependent Claim
47 words
A barrier isolating device as claimed in claim 8 wherein said voltage detecting means comprises a resistive voltage divider connected in parallel with said voltage source, the intermediate junction of said voltage divider being connected to the base of said input transistor means through a zener diode.
Claim 11
Dependent Claim
42 words
A barrier isolating device as claimed in claim 8 wherein said voltage detecting means comprises a zener diode in series with a resistive voltage divider, the intermediate junction of the voltage divider being connected to the base of said input transistor means.
Claim 12
Dependent Claim
63 words
A barrier isolating device as claimed in claim 8 wherein said current detecting means comprises resistive means connected in series with the load and means for applying the voltage across said resistive means to the base-emitter circuit of said input transistor means, whereby when said load current increases, the voltage across the resistive means also increases and turns on said input transistor means.
Claim 13
Dependent Claim
44 words
A barrier isolating device as claimed in claim 11 wherein said resistive means is connected at one end to the emitter of said input transistor means, and at the other end through a second resistive means to the base of the input transistor means.
Claim 14
Dependent Claim
52 words
A barrier isolating device as claimed in claim 11 wherein said input transistor means comprises first and second transistors having their collectors and emitters connected together, the base of the first transistor being connected to said voltage detecting means, and the second transistor having its base-emitter circuit connected across said resistive means.
Claim 15
Dependent Claim
59 words
A barrier isolating device as claimed in claim 2 wherein said current control means includes diode means in series with said load and forward biassed by said voltage source, whereby a voltage overload of opposite polarity to that of the voltage source and exceeding its value will open said diode means and disconnect the load from the voltage source.
Claim 16
Dependent Claim
44 words
A barrier isolating device as claimed in claim 2 wherein said current control means includes a controllable element and means for supplying a bias signal to the controllable element, said bias signal means receiving power from said voltage source through said first isolating means.
Claim 17
Dependent Claim
54 words
A barrier isolating device as claimed in claim 1 wherein said current transformer for transmitting signal changes between the load and the load-associated device has different numbers of turns on its primary and secondary coils, said second isolating means further comprising a range adjustment resistor connected to the secondary side of the current transformer.
Claim 18
Dependent Claim
25 words
A barrier isolating device as claimed in claim 1 wherein said load-associated device is a controller and wherein the load is responsive to the controller.
Claim 19
Dependent Claim
24 words
A barrier isolating device as claimed in claim 1 wherein the load is a sensor and the load-associated device is responsive to the sensor.
References Cited (Backward Citations)
US3582713A
Cited
US3684924A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-06-17 | 1977-12-17 | 1978-06-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-06-17 | 1981-12-17 | 1982-06-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-06-17 | 1985-12-17 | 1986-06-18 | $7700.00 | Window Closed / Lapsed |